Arshes Nei was born around 100 years prior to the events of the Bastard!! manga. As a Human/Dark Elf hybrid, she was already an outcast at her birth, as both societies were reluctant to accept her. The Dark Elf clan she lived with belittled her and jumped at the first opportunity to abandon her when conflict broke out between her clan and the Wood Elves.

A child on her own, Arshes Nei came upon Dark Schneider, grabbing at his cape. Feeling a rare sense of pity, the wizard took her in, raising her as his own daughter. This facet is more fully explained in Volume 11. It was revealed that Nei was her given name and meant "no" or "not true." Dark Schneider subsequently gave her the name Arshes and he is the only one allowed to address her as such. When she came of age, she became his lover as well. In his conquest of the world, Arshes was one of his chief commanders, the first of the Riders of Havoc to join him.

Arshes Nei is still one of the Four Riders of Havoc as the current timeline begins. Her own chief underlings are Sean Hari, Kai Harn, and the Vampire Dai Amon. She granted the first two their power. After Ninja Master Gara betrays the Riders of Havoc and rejoins the resurrected Dark Schneider, Nei is assigned to defeat him by Dark Priest Abigail and Ice Lord Kal Su. When her underlings fail, she is left to take him on herself, but only after Abigail ensures her loyalty with the Curse of the Accused, in order to prevent her betrayal, as he knew that Arshes was by far the closest to Dark Schneider out of all of the Riders of Havoc in the past.

Her subsequent fight with Dark Schneider is an intense affair, with Metallicana suffering as a side effect of their battle. Arshes Nei's feelings for Dark Schneider begin to resurface. She wishes for Dark Schneider to kill her in a duel with Halloween so she won't suffer Accused's effects: being turned into a toad. However at the last moment before the curse takes hold, Dark Schneider rips his own heart out and sprinkles Arshes with his blood, breaking Accused.

At that point, Arshes rejoins him to prevent the awakening of Anthrax. She fights with him against Abigail, and then joins him and the other riders on the Arc after Anthrax's awakening and the subsequent invasion of the Angels of Heaven after the two year time skip.

After the four-year time skip between volumes 19 and 20, her exploits are relatively unknown. She did make a brief appearance in volume 24 along with Kall-Su.

Magic: As a magician, Arshes Nei is formidable. She is a master of air elemental magic, specializing in spells involving lightning. So much so that she is known as the "Thunder Empress." She is said to be nearly as powerful as Dark Schneider, and given the fact that she fought well against him this is sustained. Via her empowerment of Sean Hari and Kai Harn, it is implied that she is skilled in High Ancient and Charm magic as well. She is also familiar with Fire Magic, though she does not specialize in it as Dark Schneider does.

Spells:

Iron Lightning Anthem: Creates magic arrows of energy that will always hit their target unless a powerful barrier is up to shield the enemy.

Swordsmanship: Arshes Nei is also an adept swordsman, and her skill exceeds Dark Schneider's in that area. Her blade, the Raijin-Ken, the Lightning God Sword inhabited by the Nue elemental is able to cut through mountains and even regenerate after it has been broken. She was seen easily destroying buildings with her sword.

Arshes' story is rather identical in the anime as in the manga, though she only engages in one fight with Dark Schneider instead of two, and fights with Abigail only, not the highest three undead that he unleashes in the manga.